Recirculating combustion apparatus jet pump

ABSTRACT

A combustion apparatus for a gas turbine engine includes a Coanda effect jet pump by which air introduced for combustion recirculates combustion products into the combustion zone of the apparatus. The jet pump is effective to improve the recirculation ratio while maintaining an acceptably low pressure drop in the combustion apparatus. The combustion air flows through the interior of the body of the Coanda nozzle and over a wall which terminates in a lip converging toward the radial surface of the Coanda nozzle body. A ring of vanes bridges the nozzle and aligns the nozzle walls. The vanes are at an angle to the radial direction to impart swirl to the primary air and improve jet pump performance.

ilnited States Patent [191 Brandon et al.

[111 3,826,083 July 30, 1974 RECIRCULATING COMBUSTION APPARATUS JET PUMP[75] Inventors: Harold J. Brandon, St. Louis, Mo.;

Wilson C. Spicer, Plainfield, lnd.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: July 16, 1973 [21] Appl. No.: 379,448

[52] US. Cl 60/39.65, 60/DIG. 11, 239/DIG. 7, 417/171, 417/197, 417/198,431/116 [51] Int. Cl. F02c 3/00 [58] Field of Search 60/3952, 269, 271,231,

60/3965, DIG. 11;417/196198, 171,151, 194; 239/D1G. 7, 265.17; 137/803;431/116;

[56] References Cited UNITED STATESPATENTS 3,041,010 6/1962 Foster417/171 X 3,319,692 5/1967 Reba et al 431/116 3,744,242 7/1973 Stettleret al. 60/DlG. 11

Primary Examiner-Carlton R. Croyle Assistant ExaminerRobert E. GarrettAttorney, Agent, or Firm-Paul Fitzpatrick [5 7] ABSTRACT A combustionapparatus for a gas turbine engine includes a Coanda effect jet pump bywhich air introduced for combustion recirculatescombustion products intothe combustion zone of the apparatus. The jet pump is effective toimprove the recirculation ratio while maintaining an acceptably lowpressure drop in the combustion apparatus. The combustion air flowsthrough the interior of the body of the Coanda nozzle and over a wallwhich terminates in a lip converging toward the radial surface of theCoanda nozzle body. A ring of vanes bridges the nozzle and aligns thenozzle walls. The vanes are at an angle to the radial direction toimpart swirl to the primary air and improve jet pump performance.

1 Claim, 6 Drawing Figures RECIRCULATING COMBUSTION APPARATUS JET PUMPOur invention is directed to combustion apparatus, particularly such asoperates at substantially superatmospheric pressure; it is moreparticularly directed to an improved jet pump in such combustionapparatus for causing recirculation of combustion products from theoutlet to the inlet of a zone in which combustion takes place.

Reba et al. U.S. Pat. No. 3,319,692, May 16, 1967, teaches recirculationof combustion products in an oil burner by a Coanda-type pump to obtainmore complete combustion and thus minimize unburned hydrocarbons, carbonmonoxide, and smoke.

Recirculation has also been proposed as a means to reduce nitrogenoxides generated in the combustion apparatus by the reaction of nitrogenand oxygen from the atmosphere in a high temperature combustion zone.The amount of nitrogen oxide generated increases with increasedtemperature and with increasing concentration of oxygen in thecombustion zone; also with time of residence in the hot zone. Byrecirculating combustion products, the concentration of oxygen in thecombustion zone may be lowered and also the temperature may be loweredto some extent. This concept is described in the copending applicationsof Stettler and Verdouw, Ser. No. 202,191 filed Nov. 26, 1971 forCombustion System and Ser. No. 220,607 filed Jan. 25,

1972, now U.S. Pat. No. 3,744,242, for Recirculating Combustor, both ofcommon ownership with this application.

Our present invention may be regarded primarily as an improvement on thecombustion apparatus of Ser. No. 220,607, the improvement residing in amore efficient and effective Coanda effect jet pumping structure forrecirculating the combustion products.

To minimize nitrogen oxides a relatively high recirculation ratio isdesired, of the order of two or better. The recirculation ratio is theratio of flow per unit time of recirculated combustion products to flowof primary combustion air entering the combustion apparatus. This is tobe distinguished from dilution air which is mixed with the combustionproducts at the termination of combustion. It is important to effect therecirculation with a minimum of pressure loss in the combustionapparatus, because pressure drops in the combustion apparatus detractfrom the efficiency of the gas turbine engine. It is also desirable thatthe recirculation ratio remain substantially constant over a wide rangeof flow rates as the output of the combustion chamber is varied to varyengine power output.

The combustion apparatus described in Ser. No. 220,607 includes a jetpump of the Coanda type disposed near the downstream end of thecombustion zone of the combustion apparatus to introduce the freshcombustion air and entrain with it combustion products which arerecirculated into the upstream end of the combustion apparatus.

The principal object of our present invention is to provide an apparatusof the type described in Ser. No. 220,607 which is more efficient andbetter meets the requirements of practice. It is a further object toprovide a jet pump for such an installation which has better efficiencythan those previously known.

The nature of our invention and its advantages will be apparent to thoseskilled in the art from the succeeding detailed description of thepreferred embodiment of the invention and the accompanying drawings.

FIG. 1 is a schematic illustration of a gas turbine combustion apparatusin axial section view.

FIG. 2 is an enlarged axial sectional view of the jet pump portion ofthe combustion apparatus.

FIG. 3 is a fragmentary sectional view taken on the plane indicated bythe line 3-3 in FIG. 2.

FIGS. 4, 5, and 6 are curves illustrating the effect of primary airswirl on jet pump operation.

FIG. 1 illustrates a combustion apparatus 2, which preferably is ofcircular cross section. The apparatus includes an outermost wall 3 whichextends from an inlet 4 for combustion air substantially to an outlet 6for combustion products from the combustion apparatus. An innermost wall7 defines a combustion zone 8 having an upstream end at 10 and adownstream end at 11. At its upstream end the wall 7 is connected by atoroidal manifold 12 to an inner wall 14 generally surrounding theinnermost wall 7. Manifold 12 is connected by a number of spacedcombustion air tubes 15 (six as shown) to a forward wall 16 disposednear the air inlet 4.

The forward wall connects tubes 15 to an outer wall 18 lying closelywithin the outermost wall 3. Wall 18 is supported from wall 3 by meanswhich need not be described. Wall 18 converges into a discharge portion19 extending into the outlet 6 and which defines a dilution zone 20.Some of the air introduced through inlet 4 flows through the annularpassage 22 between walls 3 and 18 and through holes 23 into the dilutionzone. Ad-

ditional air may flow through smaller openings as indicated by thearrows at 24. If desired, means may be provided for varying the quantityof dilution air, indicated schematically as a rotatable ring 26 havingopenings 27 variably registrable with the holes 23 in the wall 18.

The primary combustion air flows from the inlet 4 through tubes 15 intomanifold 12 and then through a primary air. passage 28 between walls 7and 14 to a C0- anda nozzle type jet pump 30. The pump includes a body31 defined by the incurved downstream end of wall 14 and a lip 32defined by the outcurved downstream end of wall 7. Primary airdischarged through the nozzle 34 between the body and lip flows upstreamthrough the recirculation passage 35 defined between walls 14 and 18 andthen, as indicated by the arrow 36, between tubes 15 into the combustionzone 8. Fuel is introduced through a nozzle 38 supplied from anysuitable source and is ignited by suitable means (not illustrated).Combustion products flow through the outlet at the downstream end 11 ofthe combustion zone. As indicated by arrow 39, a portion of thesecombustion products are entrained and pumped by the flow from jet nozzle34 into the recirculating passage. Preferably, approximately 2% times asmuch combustion products are recirculated as the flow of primarycombustion. air through duct 28. The remainder of the combustionproducts flow to the dilution zone 20 where additional air is mixed withthem and the resulting mixture is discharged through the outlet 6.

Except for the difference in the Coanda nozzle structure and therepresentation of control of dilution air, the structure described aboveis essentially the same as that described in structural detail in theprior application Ser. No. 220,607, and there is no need to enlarge upondetails of this structure to understand the present invention.

Referring now to FIGS. 2 and 3, the structure and proportions of theCoanda nozzle jet pump are more fully described. FIG. 2 shows the outerwall 18, inner wall 14, and innermost wall 7, the annular primary airpassage 28, and the annular recirculating passage 35. Wall 7 terminatesin a lip 32 which has a forward surface defining a bounding wall 40 ofone side of the annular jet nozzle 34. The terminal portion of the outerwall 18 defines the body 31 of the jet pump which curves inwardly andterminates in the forward bounding wall 42 of the nozzle. It will benoted that walls 40 and 42 converge toward each other in the directionof flow so that the minimum width of the nozzle is at the point ofdischarge.

The nozzle 34 is bridged by a ring of small sheet metal vanes 44 whichmay be brazed or otherwise fixed to the body 31 and lip 32. The vanespreserve the concentricity of the walls 7 and 14 and maintain precisespacing of the walls of the nozzle around the circumference of thenozzle.

We have found that, by inclining the vanes 44 to the radial direction,the operation of the Coanda nozzle recirculating pump is improved. Inthe specific example described, the vanes are inclined at to the radialdirection as indicated in FIG. 3. The vanes should be close enoughtogether to assure that they impart uniform swirl to the air beingdischarged and, in this case, the vanes are spaced 8 apart for a totalof 45 vanes around the circumference of the nozzle. While the vanescould be streamlined, in the particular example illustrated they aresimple sheet metal plates inch long in the radial direction, 0.09 inchwide, and 0.03 inch thick.

In the operation of the combustion apparatus, the primary air admittedthrough passage 28 is discharged through the annular nozzle 34 with acircumferential component of velocity as well as the radial one. Thisair follows the surface of the body 31 through the Coanda nozzle throatat 46 and on into the diverging diffusing portion 47 of therecirculation passage 35. This primary air flowing over the bodyentrains with it combustion air which flows forwardly over the outersurface 48 of the lip 32.

It is believed that the improved performance of the Coanda nozzle withthe swirl vanes may be due to the following reason. With the more orless spiral flow over the nozzle body, the contact'surface between theprimary and induced streams is significantly increased and thesubsequent viscous forces between the two streams should be increased.

FIGS. 4, 5, and 6 are plots of measured velocity profiles at the throat46 of the jet pump with primary air flow rates of 3/10, 4/10 and 5/10pounds per second respectively. The abscissa is velocity and theordinate is the radial distance from the centerline of the nozzle acrossthe throat. As will be seen, with zero inlet swirl there is a quitenon-uniform velocity distribution with quite high velocity over theinner half of the annulus and much lower velocity over the outer half.On the other hand, with the 20 inlet swirl, the velocity profile is muchmore uniform.

Comparative tests of air flow with strictly radial vanes and with thevanes inclined as illustrated in FIG. 3 indicate a significant increasein the ratio of secondary air to primary air with the swirling flow-anin crease of the order of 10 percent.

The more uniform velocity profile and greater ratio of induced toprimary air flow indicate the superiority of the Coanda nozzleconfiguration with the vanes 44 inclined to the radial direction.

The detailed description of the preferred embodiment of the inventionfor the purpose of explaining the principles of the invention are not tobe considered in any limiting orrestricting sense, as many modificationsmay be made by the exercise of skill in the art.

We claim:

. 1. A combustion apparatus comprising, in combination, an innermostwall defining a combustion zone having upstream and downstream ends, aninner wall defining an annular air passage with the innermost wall, anouter wall defining with the inner wall an annular recirculation passagefrom the downstream to the upstream end of the combustion zone anddefining a discharge passage from the combustion zone, and an outermostwall defining a dilution air passage with the outer wall to conduct airinto the discharge passage; the downstream end of the inner wall beingcurved inwardly and the downstream end of the innermost wall beingcurved outwardly to define a Coanda nozzle en- 'circling the downstreamend of the combustion zone between the said curved ends adapted todischarge into the recirculation passage and entrain combustion productsdischarged from the combustion zone into the recirculation passage;characterized by a Coanda nozzle structure in which the bounding wallsconverge radially from the combustor axis toward an annular radialoutlet and including a ring of swirl vanes extending between thebounding walls and directed at an angle to the radial direction so as todeliver the air from the nozzle with a circumferential component ofvelocity.

1. A combustion apparatus comprising, in combination, an innermost walldefining a combustion zone having upstream and downstream ends, an innerwall defining an annular air passage with the innermost wall, an outerwall defining with the inner wall an annular recirculation passage fromthe downstream to the upstream end of the combustion zone and defining adischarge passage from the combustion zone, and an outermost walldefining a dilution air passage with the outer wall to conduct air intothe discharge passage; the downstream end of the inner wall being curvedinwardly and the downstream end of the innermost wall being curvedoutwardly to define a Coanda nozzle encircling the downstream end of thecombustion zone between the said curved ends adapted to discharge intothe recirculation passage and entrain combustion products dischargedfrom the combustion zone into the recirculation passage; characterizedby a Coanda nozzle structure in which the bounding walls convergeradially from the combustor axis toward an annular radial outlet andincluding a ring of swirl vanes extending between the bounding walls anddirected at an angle to the radial direction so as to deliver the airfrom the nozzle with a circumferential component of velocity.